Method of fabricating casing structures for shock absorbers and the like



. l G. R. PENNINGTON 2,040,152 METHOD OF FABRICATINGCASING STRUCTURESFOR SHOCK ABSORBERS AND LIKE I Original Filed Nov. 20, 1930 m m WATTORNEY.

Patented May 12, 1936 UNITED STATES PATENT OFFICE METHOD OF FABRICATURES FOR THE LIKE TING CASING STRUC- SHOCK ABSORBERS AND signor toPennington Engineering Company,

Cleveland, Ohio, a corporation of Ohio Original application No vember20, 1930, Serial No. 496,909, now Patent No. 2,009,677, dated July 30,1935.

Divided and this application July 1, 1935, Serial No. 29,185

3' Claims. (Cl. 29*152) The invention relates to methods of fabricatingcasing structures of hydraulic shock absorbers; pumps, motors and thelike and particularly such casing structures in which a piston of thevane or swinging type is employed. Thepresent application is a divisionof my earlier application Serial No. 496,909, filed November '20, 1930issued as Patent No. 2,009,677 on July 30, 1935;

Prior to the invention covered by my application Serial No. 496,909, thecasing structures of vane-type shock absorbers were commonly made withtwo main wall parts, onepart forming the wall to engage one side and:the wall to engage the outer periphery of the piston vane, while theother partfcrmed the: wall to engage the other side of the vane. Thefabrication of such casing structures, and particularly of the integralpart forming one side wall 'and the peripheral wall, presented seriousdifliculties which I overcome by forming the :side walls :and the:peripheral wall in three separate parts.

The object of my present invention is the provision of a method by whichthe parts of a casing structure of the three-part type referred to canrapidly and at low cost bemachined to'accurate dimensions for propercooperation with the piston and shaft structure of the device.

To facilitate explanation" of my improved methodI have shown in theaccompanying drawing one of the several forms of 'casingconstructionillustrated in my said application Serial No. 496,909 together with anassembly' plug which is employed in carrying outthe method.

In the drawing,.Fig.' 1 is a sectional view of the casing of a shockabsorber of the vane type to which my "improved method is applicable.

Fig. 2 is a front elevation of the casing.

Fig. 3 is a section on the. line '3-3 .of Fig. 1 showing in'the chamberof'the casing an assembly plug suitable for use :in carrying out mymethod.

Fig. 4 is a fragmentary section on the line 4-4 of Fig. 2.

Fig. 5 is a side elevation of the assembly plug shown in Fig. 3.

To facilitate an understanding of the method I shall first describe thecasing rstructure illustrated in the drawing."

The structure comprises 'a rear plate-like part I which is circular inform, an intermediate part 2,-and a front plate-like. part 3. Thesecasing partsmay be made of anysuitablemetal. I prefer to make them inthe form of steel forgings but they may also be made in the form ofmalle- :able ironcastings $til1 other metals may. be

found satisfactory. The parallel side surfaces of the intermediate part2 are made to nicely fit the adjacent plane surfaces of the rear andfront parts and the three parts are tightly and rigidly secured togetherby cap screws 4, 4 and dowel bolts 5, 5, said bolts being of suitablelength to project through a vehicle frame part (not shown) so that whenthe nuts 5 of the bolts are tightened up they clamp the casing tothevehicle frame as well as help secure the casing parts together. The capscrews pass loosely through apertures in the front part 3 and theintermediate part 2 and engage threaded closed bottom holes in the rearpart I (Fig. 4). The dowel bolts 5 engage apertures in the front casingpart 3 and the intermediate casing part 2 with suitable fits for dowelmembers and engage apertures in the rear casing part I with relativelyheavy forced fits, the object of the very close fits in the rear part Ibeing to obviate leakage. The dowel bolts 5 approach from the rear faceof the shock absorber casing and thus serve as a means for securing thecasing to a frame of the vehicle, as well as helping to secure the threeparts of the casing together and serving, as dowels, to accuratelyposition the three casing parts in relation to each other.

Casing structures of this character comprise an additional reservoirmember which has not been shown as it is not involved in the practice ofthe present invention.

The casing part 2 forms the peripheral wall of an approximately sectorshape chamber which is designed to receive a piston of the swinging orvane type, the vane being mounted on or integral with a shaft. The frontcasing part 3 is provided with a bearing boss 3 through which the pistonshaft extends and which is provided with a suitable anti-frictionbushing 3 The rear member I of the casing is bored out and fitted with abushing I to provide a bearing for the rear end of the shaft. Theintermediate part 2 of the casing is formed with concentric circularsurfaces 2 and 2 designed to engage the hub and outer peripheralsurfaces, respectively, of the piston or vane, the surfaces 2"- and '2being concentric with the bearings in the members I and 3.

I turn now to the method of machining and fabricating the casingstructure. By making the main casing in three parts, I, 2, and 3, it ispossible to have the two joints between these three parts formed byplane surfaces which can be accurately machined with great ease andrapidity. This machining I preferably carry out by grinding operationson the three casing parts. The peripheral surfaces 2 and 2 of the casingpart 2 I machine or finish by a simple broaching operation, it beingpossible to form both of the concentric surfaces simultaneously by asingle breaching tool. This operation is, of course, made possible bythe fact that the casing part 2 is separate from both of the parts I and3.

To insure proper alignment and relative positioning of the two shaftbearings when finished with the finished surfaces 2 and 2 of the casingI have devised a special procedure. First, the plane surfaces of thethree casing parts I, 2, and 3 are machined and the internal surfaces ofthe intermediate part 2 are broached, as above described. The holes forthe cap screws and the dowel bolts are then drilled in the back plateand the front plate, the bolt holes being drilled about 2" under sizeand the screw holes in the front plates about over size, and the screwholes in the back plate are tapped. The back plate is then placed in afixture which locates the plate in relation to the bolt holes thereinand the rear hearing recess is bored out, the bushing thereof insertedand finish bored. Then, in the same man ner, the shaft bearing of thefront plate is machined. The middle casing part 2 is placed in a fixturewhich locates the part with respect to the broached surfaces thereof andthe holes for the cap screws and the dowel bolts are drilled. The boltholes are drilled about 2" under size and the screw holes about E oversize, as in the case of the front plate of the casing.

Next the three casing parts I, 2, and 3 are assembled upon a fixture A(Fig. 5) which I term an assembly plug. This assembly plug comprises amain shaft section A to engage the bearing of the front casing plate 3and a rear shaft section A to engage the bearing of the rear casingplate I. It also comprises a vane part A having a hub portion A Theassembly plug is similar to the combined piston and shaft of the shockabsorber except that the vane or piston part A has a circumferentialextent great enough to substantially fill the working chamber of theshock absorber and that the fixture is made of such a size that itsbearing surfaces which engage the peripheral surfaces 2 and 2 of thecasing part 2 fit the latter with a smaller clearance than do thecorresponding surfaces of the shock absorber piston. This assembly plug,being made very accurately, serves to very accurately position thesurfaces 2 and 2 of the intermediate casing part in relation to theshaft bearings of the casing parts I and 3.

The three casing parts when assembled upon the plug A are brought intoalignment with each other by inserting a pin through one of the sets ofholes and then while the three casing parts are clamped rigidly togetherthe dowel bolt holes are brought to their final finished size byreaming, the bolt holes in the back plate I being preferably finished toa somewhat smaller size than the bolt holes in the other two casingmembers so that the dowel bolts when they are inserted in the assembledcasing will have a heavy pressed fit in the back plate that will insurea leak tight joint or engagement between the bolts and the said backplate. With the casing parts thus machined, it is obvious that when theshock absorber is assembled the insertion of the dowel bolts willposition the three casing parts with a high degree of accuracy in theirproper relation to each other.

It will be obvious to those familiar with modern machine tool practicethat my improved casing structure can be machined in the mannerdescribed with very great ease and facility with a high degree ofaccuracy and uniformity so that a nice working fit between the bearingor working surfaces of the piston and shaft member and of the casing isinsured.

The machining of the peripheral walls of the sector-shape chamber of themain casing of the shock absorber is highly advantageous because itcombines low cost with a high degree of accuracy. This method is madepossible by the three-part construction of the main casing and by thenovel method of machining the dowel holes with reference to the broachedsurfaces.

While I prefer to proceed in the manner above described it will beobvious to those familiar with machine tool practice that the procedurecan be varied in different ways without departing from the invention asdefined in the appended claims.

What I claim is:

1. The method of machining the casing of a vane-type shock absorber orthe like having front and rear wall parts with plane surfaces to engagethe sides of the vane and with a shaft-bearing aperture in at least oneof said parts, an intermediate part having concentric surfaces to engagethe hub and outer periphery, respectively, of the vane and plane frontand rear surfaces to engage the front and rear wall parts, and dowelsengaging the three casing parts, the said method comprising forming theconcentric surfaces of the intermediate part and the bearing aperture orapertures of the front and rear parts, securing the three parts togetherwith the bearing aperture or apertures in axial alignment with theconcentric surfaces of the intermediate part, and while the three partsare so secured accurately forming aligning dowel holes in all threeparts.

2. The method of machining the casing of a vane-type shock absorber orthe like having front and rear wall parts with plane surfaces to engagethe sides of the vane and with a shaft-bearing aperture in at least oneof said parts, an intermediate part having concentric surfaces to engagethe hub and outer periphery, respectively, of the vane and plane frontand rear surfaces to engage the front and rear wall parts, and dowelsengaging the three casing parts, the said method comprising forming theconcentric surfaces of the intermediate part, drilling dowel holes inthe front and rear wall parts to undersize dimensions, forming a shaftbearing aperture in one or both of the front and rear wall parts in aposition located from the dowel holes of such part, drillingcorresponding undersize dowel holes in the intermediate part of thecasing while said part is located with respect to the concentricsurfaces thereof, securing the three parts together with the bearingaperture or apertures in accurate axial alignment with the concentricsurfaces of the intermediate part and with the corresponding dowel holesof the three parts in alignment, and while the three parts are sosecured accurately forming the aligning dowel holes of all three partsto their full finished dimensions.

3. The method-of machining the casing of a vane-type shock absorber orthe like having front and rear wall parts with plane surfaces to engagethe sides of the vane and with a shaft bearing aperture in at least oneof said parts, an intermediate part having concentric surfaces to engagethe hub and outer periphery, respectively, of the vane and plane frontand rear surfaces to engage the front and rear wall parts, dowelsengaging the three casing parts, and screws passing through the frontand intermediate parts and having threaded engagement with the rearpart, the said method comprising forming the concentric surfaces of theintermediate part, drilling in the front and rear wall parts dowel holesto undersize dimensions and screw holes, the screw holes in the frontplate being drilled oversize, forming a shaft bearing aperture in one orboth of the front and rear wall parts in position located from the dowelholes of such part, drilling undersize dowel holes in the intermediatepart corresponding to the dowel holes of the front and rear parts andlocated with respect to the concentric surfaces of the intermediate partand simultaneously drilling oversize screw holes in the intermediatepart corresponding to the screw holes of the front and rear parts,securing the three parts together with the hearing aperture or aperturesin accurate axial alignment with the concentric surfaces of theintermediate part and with the corresponding dowel and screw holes ofthe three parts in alignment, and while the three parts are so securedaccurately forming the aligning dowel holes of all 10 three parts totheir full finished dimensions.

GORDON 'R. PENNINGTON.

